Roller cone or rotary cone bits are well known in the art of earth boring drilling operations. The most common design of a roller cone bit consists of three roller cones, each rotatably mounted on a downwardly and radially inwardly extending bearing pin. Each roller cone supports a plurality of cutting elements, which are referred to as cutters. Each of the bearing pins is spaced approximately 120 degrees apart with the three pins formed as a part of a bit body. The entire structure is rotated at the end of a drill string. Boring is accomplished by applying weight to the drill bit and rotating the drill string, thereby causing the roller cones to roll and crush the rock formation beneath the bit. As the bit is rotated and moves through a formation, the cutter elements contact and disintegrate portions of the formation in order to form the desired bore hole. The earth separated from the formation become cuttings that are removed from the bottom and sides of the bore hole and washed away by a drilling fluid, such as air or drill mud, that is supplied to the drill bit from the surface through the hollow rotating drill string. The cuttings are suspended in the drilling fluid and carried to the surface in the space between the bore hole and the drill string.
The cuttings produced by the drilling operation are abrasive and with continued use will erode the cutters and other portions of the bit. The grinding and re-grinding of the cuttings produced by the drilling operation slows the formation penetration rate of the bit and shortens the life of the bit. The re-ground cuttings tend to dull the cutters and the finely ground particles may enter the bearing surfaces formed between the roller cones and the journals supported by the bit, restricting cutter cone rotation and further limiting bit life.
Reference is made to U.S. Pat. No. 6,082,473 to Dickey, which is incorporated herein by reference and discloses a self-cleaning polycrystalline diamond compact (PDC) bit.
Reference is also made to U.S. Pat. No. 5,462,128 to Gray, which is incorporated herein by reference and discloses a cutter bit having a passageway for cuttings to escape to the surface of the hole.
Further reference is made to U.S. Pat. Nos. 2,692,117 and 3,099,324 each to Kucera which disclose drill bits having passageways through the bit for the evacuation of cuttings.